Dietary Salt in Postural Tachycardia Syndrome

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government.
Read our disclaimer for details.

Patients with POTS may not adequately expand their plasma volume in response to a high-sodium diet. Mechanisms involved in the regulation of plasma volume, such as the renin-angiotensin-aldosterone system and renal DA, may be impaired in POTS and may respond inappropriately to changes in dietary sodium.The purpose of this study is to determine (1) whether a high dietary sodium level appropriately expands plasma volume in POTS; (2) whether plasma renin activity and aldosterone are modified appropriately by changes in dietary sodium in POTS; and (3) whether patients with POTS have improvements in their orthostatic tachycardia and symptoms as a result of a high dietary sodium level.

This will be done after supine assessment, but before standing the subject up

Autonomic Function Test with Cardiac Output and Brief Tilt

The subject will be tilted up to 60-75 degrees head-up tilt for up to 10 minutes to measure the changes in heart rate and blood pressure and symptoms with upright challenge.

Blood volume - carbon monoxide rebreathing

Exercise Capacity Test (in the afternoon) Will estimate maximal oxygen consumption (VO2 max) This test will be conducted on a stationary bicycle. Effort will be gradually increase while expired air is measured during exhaustive physical work.

All procedures are repeated at least a month later with the 2nd level of dietary salt. (Randomized to high or low salt to the first phase, the second phase is the remaining level)

POTS and healthy controls will be randomly assigned the order of dietary sodium levels. All procedures are performed at both levels.

Radiation: Blood Volume

we will measure the amount of hemoglobin and myoglobin in the body by a procedure called carbon monoxide (CO) rebreathing. One teaspoon of blood is taken before and after a small amount of CO has been absorbed into the bloodstream.

subjects breath room air through a mouthpiece and exhale the air into a tube that connects to a machine (metabolic cart) that analyzes carbon dioxide and oxygen content, which allows the investigator to calculate the amount of oxygen they are using under resting and exercise conditions.

Other Name: VO2 Max (maximal oxygen consumption)

Procedure: Posture Study

Blood pressure and heart rate will be measured while supine and then while standing for up to 30 minutes. Blood will be drawn in each position to measure hormones that regulate blood pressure and blood volume.

Other Name: Standing Orthostatic Challenge

Experimental: Low Sodium Dietary Level

Radiation: Blood Volume

we will measure the amount of hemoglobin and myoglobin in the body by a procedure called carbon monoxide (CO) rebreathing. One teaspoon of blood is taken before and after a small amount of CO has been absorbed into the bloodstream.

subjects breath room air through a mouthpiece and exhale the air into a tube that connects to a machine (metabolic cart) that analyzes carbon dioxide and oxygen content, which allows the investigator to calculate the amount of oxygen they are using under resting and exercise conditions.

Other Name: VO2 Max (maximal oxygen consumption)

Procedure: Posture Study

Blood pressure and heart rate will be measured while supine and then while standing for up to 30 minutes. Blood will be drawn in each position to measure hormones that regulate blood pressure and blood volume.

blood volume [ Time Frame: after 7 days of each dietary sodium level ]

DAXOR (131-I labelled albumin) blood volume assay

Secondary Outcome Measures
:

Magnitude of suppression of aldosterone (from low sodium to high sodium diets) and a reduction in orthostatic tachycardia and orthostatic symptoms in POTS patients with the high-sodium diet. [ Time Frame: after 7 days of each dietary sodium intervention ]

Whether plasma renin activity and aldosterone are modified appropriately by changes in dietary sodium in POTS & whether patients with POTS have improvements in their orthostatic tachycardia and symptoms as a result of a high dietary sodium level.

Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study. To learn more about this study, you or your doctor may contact the study research staff using the contacts provided below. For general information, Learn About Clinical Studies.